This invention relates to photographic film processing apparatus and, more particularly, it concerns an improved doctoring surface for use in an applicator nozzle structure for depositing a uniform layer of processing fluid on a moving run of cassette contained photographic film.
Motion picture systems in which exposure, processing and projection operations are carried out on a film strip contained at all times in a multipurpose cassette are disclosed in several issued U.S. patents, assigned in common with the present invention. In these systems, the strip of film, as supplied with the cassette, is initially wound on a supply spool and advanced to a takeup spool when the cassette is placed in an appropriate camera for exposure in essentially conventional fashion. Following exposure, the cassette is placed into a viewing apparatus capable of activating a cassette contained processor to deposit a uniform layer or coating of processing fluid along the length of the film strip as it is rewound from the takeup spool back to the supply spool. Thereafter, a series of successive transparent image frames formed on the film strip may be viewed by projection and rewound for subsequent projection cycles as desired.
The achievement of a uniform layer or coating of processing fluid on the film strip during the processing operation is vital to overall system operation and has been a major focal point of attention in overall system development. The current state of the art with respect to achieving a uniform coating of processing fluid on such cassette contained film strips is represented by the disclosures of U.S. Pat. Nos. 3,871,013 issued Mar. 11, 1975 to Edward F. Burke and Douglas B. Holmes, and 3,951,530 issued Apr. 20, 1976 to Frank M. Czumak, Paul B. Mason and Joseph A. Stella, both of which patents are commonly assigned with the present invention. In the disclosures of these patents, an inclined doctoring surface is used to develop a positive hydrodynamic force in the deposited processing fluid to thereby hold the film in engagement with an underlying pressure pad; the latter being operative to support the film strip beneath the doctoring surface in a manner to provide a net balance of forces on opposite sides of the film strip. Another configuration for achieving uniform processing fluid deposition is illustrated and described in copending U.S. patent application Ser. No. 791,025, filed Apr. 26, 1977 by F. M. Czumak and P. B. Mason, entitled "Film Cassette Contained Processing Fluid Applicator Having Converging Fluid Channel", which patent application is also commonly assigned with the present invention.
Because of the need for cassette ventilation, both to dry the processing fluid and to cool the film strip during projection, and also because of the environment to which the cassette may be exposed in normal use, it is difficult, if not impossible to prevent entry of foreign particles and/or dust to the cassette material. While the presence of such particles is not a serious problem to film strip exposure and projection, it is critical to proper film strip processing that foreign particles present on the film strip be prevented from accumulating in the region of the doctoring surface by which the processing fluid is spread uniformly onto the film strip. The achievement of a net balance of forces on opposite sides of the film strip as it passes the doctoring surface in accordance with the disclosure of the aforementioned issued U.S. patents has contributed substantially to the solution of this problem by permitting the film strip carried particles to pass the doctoring surfaces without accumulation and without dragging or streaking the processing fluid in a manner to create blemishes which will appear in the viewed images of the processed film. There remains, however, a potential for accumulation or wedging of foreign particles as a result of the inclination of the doctoring surface toward its trailing end which provides a narrowing gap between the doctor blade and the film surface. A large portion of the particles present on the film strip which may accumulate and affect deposition of the processing fluid are what are referred to as "stringers" or shavings of film strip which are a product of steps carried out in the manufacture of the film strip. Such shavings of film are potentially on the order of 0.002 inch wide and up to 0.010 to 0.015 inch in length. Because of the potential of such stringers entering into the narrowing gap between the doctor blade and the film, and the resultant high probability of a degrading of the function of the doctor blade due to the size of such particles, it is deemed particularly desirable to prevent such debris from passing into the region of the doctor blade.